The polyester carbonates and methods for their preparation are described in U.S. Pat. Nos. 3,030,331; 3,169,121 and 3,207,814, all of which are hereby incorporated by reference. Generally, the methods for the preparation of these copolymers have been based on combining the monomers in an organic reaction media through which a carbonyl halide is passed.
It has now been found that the polyester carbonates can be prepared via an interfacial process that is carried out in a reaction media which comprises water and an immiscible organic solvent.
The interfacial process provides a product that has less color than the prior art processes and simplifies the recovery of the product. The byproducts of the polymerization process remain in solution throughout the process and are easily isolated from the polymer containing organic phase. It has also been discovered that only catalytic amounts of amines are necessary while prior art processes required a molar excess. The interfacial process also permits the use of inorganic base in place of the tertiary amines that were employed in the prior art processes as halogen acid acceptors. The use of inorganic bases reduces the total cost of the process.
In addition, this invention also provides novel branched polyester carbonates that include a branching agent having at least three ester forming groups.